Process of dewaxing oils by flotation



0a. 4, 1955 J. DOORN 2,719,817

PROCESS OF DEWAXING OILS BY FLOTATION Filed May 12, 1952 WAX l4\ WAX HEATER WA! on.

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INVENTOPJ- J HANNIS D ORN BY 74w /o7w-r -c ms ATTORNEY which a portion of the Wax is in United States Patent PROCESS OF DEWAXING OILS BY FLOTATION Iohannis Doom, Amsterdam, Netherlands, assignor Shell Development Company, Emeryville, Callfl, a corporation of Delaware Application May 12, 1952, Serial No. 287,405 Claims priority, application Netherlands July 26, 1951 10 Claims. (Cl. 196-18) This invention relates to a method of dewaxing waxbearing oils. More particularly, it relates to a method of dewaxingwaxy mineral oils by means of flotation.

The so-called flotation dewaxing method involves passing an inert gas through a Waxy oil at dewaxing temperatures. The solid wax occludes bubbles of cold flotation gas, and the specific gravity differential between solid wax and oil is thereby increased. The wax-coated gas bubbles then rise to the surface of the oil in the form of a foam. This wax-containing foam is readily separated from the dewaxed oil by various well-known methods, for example, by decantation.

Although the dewaxed oil obtained is substantially free from solid wax, substantial amounts of oil are entrained by the wax-containing foam, and the oil yield from the flotation dewaxing method is comparatively poor.

lt is,.therefore, a principal object of the present invention to provide animproved flotation dewaxing method. Another object is to provide a method of dewaxing oils by flotation whereby improved yields of dewaxed oil are obtained. Other objects and advantages willbe apparent from the following description.

Now, in accordance with thisinvention, it has been found that improved yields of dewaxed oil can be obtained by a flotation dewaxing method which comprises contacting a waxy oil, in a first flotation stage, with an inert flotation gas at a first temperature (T1), whereby a first wax-containing foam layer and a first oil layer are obtained, separating the first wax-containing foam layer from the first oil layer, contactingthe Wax and oil content of said first wax-containingfoam layer, in a second flotation stage, with an inert flotation gas at a second temperature (T2) which is higher than the first temperature, but at the solid state, whereby a second wax-containing foam layer and a second oil layer are obtained, separating the second wax-containing foam layer from the second oil layer, contacting said second oil layer, in a third flotation stage, with an inert flotation gas at a third temperature (T3) which is'lower than the second temperature (T2), and which'is preferably identical with the first temperature (T1), whereby a third waxcontaining foam layer and a third oil layer are obtained, and separating said third wax-containing foam layer from said third oil layer. The dewaxed oil obtained from the first flotation stage at T1 and/or from the third flotation stage at T3, can be further subjected to flotation dewaxing at a temperature (To) which is substantially lower than T1 or T3 in order to produce a wax product of substantially lower melting point than that produced in the second and/ or third flotation stages.

According to a preferred embodiment of the present invention, a waxy oil is subjected to a flotation treatment ata first temperature (T1), whereby a first wax-containing foam layer and a first oil layer are obtained, the resulting first wax-containing foam layer is separated from the first oil layer and the first wax-containing foam layer is subjected to "a flotation treatment at a second temperature 'of the foam through heater (T2) which is higher than the first temperature (T1), but at which a portion of the wax is in the solid state, whereby a second Wax-containing foam layer and a second oil layer are obtained, the second wax-containing foam layer is separated from the second oil layer, and the separated second oil layer is recycled to the flotation treatment conducted at temperature (T1).

The present process is applicable to the treatment of such materials as mineral oils or fractions thereof, hydrocarbon oils which are synthetically produced, as by catalytic reaction of hydrocarbons or by the Fischer-Tropsch reaction of carbon monoxide and hydrogen, vegetable oils containing free fatty acids, mixtures of unsaturated and saturated fatty acids, mixtures of fatty acids of difierent molecular weights, and the like.

Any gas which is inert under operating conditions can be used in the floation operation. Suitable gases include air, nitrogen, hydrogen, carbon monoxide, carbon dioxide, sulfur dioxide; methane, ethane, propane, ammonia; and the like. Ammonia is, of course, unsuitable where wax acids are present. The flotation gas may at the same time be a refrigerant. It is to be understood, however, that the primary function of the flotation gas is to separate the solid wax from the oil in the form of a foam.

The selection of the dewaxing temperatures (T1) and (T3), depends upon such factors as the particular oil fraction being dewaxed, the desired degree of dewaxing, i. e., the desired pour point of the dewaxed oil, the types of waxes present, and the like. It is preferred that temperature (T3) be identical to temperature (T1) so that the dewaxed oil obtained in the first and third stages has the same pour point. The difference between T1 and T2, and between T2 and T3 should be significant, that is, at least about one degree centigrade. V

The present invention will be better understood from the following detailed description made with reference to the accompanying drawing which is a schematic flow diagram of a flotation dewaxing operation in accordance with the present invention. For purposes of simplicity, pumps, temperature controls, control means, and other auxiliary equipment, the proper placement of which is evident to those skilled in the art, have been largely omitted.

Now, referring to the drawing, a waxy mineral oil, from a source not shown, is cooled to the desired temperature (T1), by passage through a suitable cooler 1 which may be an externally refrigerated coil. The cooled oil, containing crystallized Wax, is then introduced into column 2 at an intermediate point thereof. A suitable gas which has been brought to the desired flotation temperature is introduced by means of line 3 into the bottom of column 2 and passes through a disperser (e. g., a fine filter) 4, by means of which the gas is dispersed over the entire cross-section of the column. The gas passes upwardly carrying with it the solid wax.

The resulting wax-containing foam is Withdrawn from the top of column 2 by means of line 5, and the resulting dewaxed oil is removed from the bottom of the column through line 6. The wax-containing foam is then passed through heater 7 where it is heated to a temperature (T2) at which a portion of the wax remains in the solid state. Under some circumstances, it is desirable, in order to insure smooth running of the process, to heat the waxcontaining foam to a temperature at which all of the wax has liquefied, and then cool the liquid mixture to the desired temperature (T2) as in cooler 8, whereupon solid wax crystallizes out.

As a general rule, the entire amount of gas, or a considerable portion thereof, separates out during passage 7. The, heated mixture of oil and solid wax is then introduced into column 9 where it is contacted with a flotation gas which is introduced by means of line 3, at a suitable temperature, into the bottom of column 9. The resulting wax-containing foam is then removed from the top of column 9 by means of line 11, and is processed for recovery of wax therefrom. The dewaxed oil is removed from the bottom of the column through line 10. In some cases, the wax-containing foam produced in column 2 is very stable so that when it is passed through heater 7, a mixture of an oil phase and a foam phase are obtained. In this case, the mixture is passed to column 9 where it is permitted to stratify, and the resulting wax-containing foam and dewaxed oil are separately removed from the column. Thus, flotation is eifected without the introduction of further quantities of gas. Usually, however, it is necessary to introduce flotation gas into column 9 in order to effect flotation.

The dewaxed oil, which is discharged from column 9 through line 10, is then passed through cooler 12 wherein it is cooled to temperature (T3). The cooled oil, which now contains solid wax as a result of the cooling, is introduced into column 14 wherein it is contacted with a flotation gas which is introduced by means of line 3, at a suitable temperature, into the bottom of column 14. The resulting dewaxed oil, which is discharged from column 14 through line 15, can be combined with dewaxed oil from column 2. The resulting wax-containing foam is removed from the top of the column by means of line 16. The resulting foam can be processed for recovery of wax therefrom, or it can be combined with the wax-containing foam removed from column 9, and wax can then be recovered from the resulting foam mixture. It is preferred, however, to recycle the foam obtained in column 14, through line 17, to heater 7 for feeding column 9. Thus, reflotation of the foam from column 14 is effected without the use of another column.

It is, of course, possible to carry out the above-described process in as many stages as desired by successively subjecting a wax foam, obtained from a previous flotation operation, to flotation at a temperature higher than that of the preceding operation, and then subjecting the resulting dewaxed oil to flotation at a temperature lower than that at which the Wax foam was treated. Thus, the wax-containing foam from column 14 is heated to a temperature (T4), which is preferably identical to temperature (T2), and at which a portion of the wax is in the solid state, and is then subjected to flotation. The resulting wax-containing foam is separated from the remaining oil. The oil from the fourth flotation step is cooled to a temperature (T5), which is preferably identical to T1, and is then subjected to flotation. The oil obtained from the fifth flotation step can be combined with the oil obtained from the first and/ or third flotation steps. Likewise, the wax-containing foam from the fifth flotation step can be combined with the wax-containing foam from the second and/ or fourth flotation steps.

According to a preferred embodiment, of the present invention, dewaxed oil, discharged from column 9, is recycled through line 19 to cooler 1 for feeding column 2. In this way, flotation of the oil can be effected without the use of column 14. It is preferred to recycle the dewaxed oil from the second stage to the first stage, rather than subject it to flotation dewaxing in a separate third stage, since flotation dewaxing is more effective in the presence of the higher proportion of higher melting normal parafiins present in the first stage.

According to another embodiment of the invention, the dewaxed oil from colum 2 and/or column 14 can be treated at a temperature (To) which is substantially lower than T1 or T3, in order to produce a wax product of substantially lower melting point than that produced in the second and/or third flotation stages shown above. Referring to the drawing, dewaxed oil from lines 6 and 15, is passed through a suitable cooler 20, wherein it is cooled to a temperature (To). The cooled oil, now containing solidified wax, is introduced into column 21 at an intermediate point thereof. A suitable flotation gas which has been brought to the desired flotation temperature is introduced from line 3 into the bottom of column 21. The resulting dewaxed oil is discharged from column 21 through line 22. The resulting wax-containing foam is removed from column 21 through line 24 and is treated for recovery of wax therefrom. If desired, the wax-containing foam from column 21 can be subjected to flotation in another column (not shown) at a tempera ture which is higher than To, and in which a portion of the wax is in the solid state. The resulting wax-containing foam can then be treated for recovery of wax therefrom, and the resulting dewaxed oil can be subjected to flotation at a lower temperature, either by recycling to column 21, or in a separate column.

The following example is illustrative of the flotation method of the present invention wherein a three-stage method, without recirculation, is employed.

Example An Indonesian gas oil was cooled to about 10 C., and was then subjected to flotation by passing nitrogen therethrough for a period of about 1% hours at a rate of 1 /2 liters per hour. The resulting wax-containing foam layer and oil layer were separated. The oil layer obtained was substantially free of solid wax as was evident from its cloud point (12 C.). The oil yield from this step amounted to 79.4% by weight, based on the initial material.

The separated foam layer was then heated to 14 C., and was then subjected to flotation at this temperature, by the same method described above. The oil layer obtained as a result of this treatment amounted to about 14.9% by weight, calculated on the initial material.

The oil layer obtained in the second step was cooled to 10 C. and subjected to flotation, at this temperature, in the same manner described above. This flotation step yielded 10.6%, by Weight, based on initial material, of oil. The oil obtained in this step was combined with the oil obtained in the first step. The total oil yield amounted to 90.0%, by weight, as against 794%, by weight, as yielded by a single flotation step. Thus, by employing the sequence of operations described above, the oil yield was increased by 13.4% over a single flotation operation.

Where the oil must be cooled down to the desired temperature, the cooling can be at least partially achieved by employing a cold flotation gas. Similarly, when it is necessary to heat the wax-containing foam to the desired flotation temperature, the heating can be at least partially.

achieved by employing a heated flotation gas.

It is preferred that the viscosity of the mixture of oil and solid wax, at the operating temperatures be maintained at a value not higher than about 25 to 50 cps., depending on the nature of the oil. If necessary, diluting agents can be added. Suitable diluting agents include any of the well-known organic dewaxing solvents which are substantially miscible with the 'oil phase, but substantially immiscible with the wax phase, at dewaxing temperatures. genated hydrocarbons such as ethylene dichloride, ethylene dibromide, chloroform, carbon tetrachloride, ethyl chloride, propyl chloride, ethyl bromide, propyl bromide, trichloroethane, tetrachloroethane, propylene chloride, trimethylene chloride, amyl bromide, tertiary amyl chloride, butyl chloride, butyl bromide, allyl bromide, beta, beta dichlorodiethyl ether, chlorobenzene, bromobenzene, o-dichlorobenzene, tetrachloroethylene, tetrafluoroethylene, Z-chlorophenylamine, 3-chlorophenylamine, and 1- amino-Z-fluurobenzene; aliphatic and aromatic hydrocarbons such as petroleum ether, petroleum naphtha, gasoline, pentane, isopentane, hexane, heptanc, octane, benzene, propylbenzene, cumene, 'amylbenzene, toluene, xylene and cumene; ketones such as methyl isopropyl ketone, methyl isobutyl ketone, methyl ethyl ketone, and mixtures thereof with hydrocarbons such as benzene and/ or toluene; and, other compounds such as nitrobenzene, furfural, aniline, toluidine, o-amino-ethylbenzene,

Suitable dewaxing solvents include halo- In-amino-ethylbenzene, N-methylaniline, N-ethyl phenylamine, p-methoxyaniline, l-ethoxybutane, and methyl phenyl ether; as well as various mixtures thereof, and with other solvents.

The wax concentrate obtained by the present flotation method can be further treated, for separation of oil therefrom, by various well-known methods such as pressing, sweating or solvent dewaxing. A particularly effective dewaxing treatment comprises, briefly, mixing the solid wax (containing oil) with a dewaxing solvent and with an auxiliary liquid (water) containing an ionic surfaceactive agent, and if necessary, a demulsifier, correlating the dielectric constants of the two liquid phases so that the contact angle of the solid wax in the oil-solvent phase is at least 90, whereby the solid wax is transferred to the auxiliary phase, separating the wax-containing auxiliary phase from the oil-solvent phase, and recovering wax from the auxiliary phase. This process is described in greater detail in the copending application of Mondria et al., Serial No. 262,438, filed December 19, 1951.

I claim as my invention:

1. A method of dewaxing a waxy oil which comprises contacting said waxy oil with an inert flotation gas at a first temperature (T1), whereby a first wax-containing foam layer and a first oil layer are obtained, separating said first wax-containing foam layer from said first oil layer, contacting the wax and oil content of said first waxcontaining foam layer with an inert flotation gas at a second temperature (T2), which is higher than said first temperature (T1) but at which a portion of the wax is in the solid state, whereby a second wax-containing foam layer and a second oil layer are obtained, separating said second wax-containing foam layer from said second oil layer, and recycling said second oil layer for contact with an inert flotation gas at said first temperature (T1), the viscosities of the wax and oil at the temperatures T1 and Ta being maintained below about 50 centipoises.

2. A method according to claim 1, wherein said inert flotation gas is air.

3. A method according to claim 1, wherein said inert flotation gas is nitrogen.

4. A method of dewaxing a waxy oil which comprises contacting said waxy oil with an inert flotation gas at a first temperature (T1), whereby a first wax-containing foam layer and a first oil layer are obtained, separating said first wax-containing foam layer from said first oil layer, contacting the wax and oil content of said first waxcontaining foam layer with an inert flotation gas at a second temperature (T2) which is higher than said first temperature (T1), but at which a portion of the wax is in the solid state, whereby a second wax-containing foam layer and a second oil layer are obtained, separating said second wax-containing foam layer from said second oil layer, contacting said second oil layer with an inert flotation gas at a third temperature (T3), which is lower than said second temperature (T2), whereby a third wax-containing foam layer and a third oil layer are obtained, and separating said third wax-containing foam from said third oil layer, the method being conducted in the presence of an identical organic dewaxing solvent medium through out, the viscosities of the wax-oil-solvent mixtures at temperatures T1, T2 and T3 being less than about 50 centipoises.

5. The method according to claim 4, wherein said third temperature (Ta) is identical with said first temperature 6. The method according to claim 4, wherein said third wax-containing foam layer is recycled for contact with an inert flotation gas at said second temperature (T2).

7. The method according to claim 4, wherein said inert flotation gas is air.

8. The method according to claim 4, wherein said inert flotation gas is nitrogen.

9. A method of dewaxing a waxy oil which comprises contacting said waxy oil with an insert flotation gas at a first temperature (T1) in a first flotation zone, whereby a first wax-containing foam layer and a first oil layer are obtained, separating said first wax-containing foam layer from said first oil layer, contacting the wax and oil content of said first wax-containing foam layer with an inert flotation gas in a second flotation zone at a second temperature (T2) which is higher than said first temperature (T1), but at which a portion of the wax is in the solid state, whereby a second wax-containing foam layer and a second oil layer are obtained, separating said second waxcontaining foam layer from said second oil layer, recycling said second oil layer to the first flotation zoneand therein contacting it together with a further portion of said waxy oil with an inert flotation gas at a temperature (T1), whereby a wax-containing foam layer and an oil layer are obtained, separating the foam layer and the oil layer, and contacting the last separated combined oil layer with an inert flotation gas in a furtherflotation zone at a temperature (T4), which is lowerthan the temperature (T1), whereby a further wax-containing foam layer and a further oil layer are obtained, and separating these last named foam layer and oil layer, the viscosities of the wax and oil at temperatures T1, T2 and T4 being maintained below about 50 centipoises.

10. A method according to claim 1, wherein the waxy oil has a viscosity at the flotation temperature (T1) greater than 50 centipoises and it is diluted with an organic dewaxing solvent suflicient to reduce the mixture of oil and solid wax at the operating temperature to a value not higher than 50 centipoises.

References Cited in the file of this patent UNITED STATES PATENTS 1,277,935 Hussey Sept. 3, 1918 1,848,636 Livingstone Mar. 8, 1932 2,229,659 Carr Jan. 28, 1941 2,265,139 Brandt Dec. 9, 1941 2,314,994 Lawson et a1 Mar. 30, 1943 2,645,598 Myers et a1 July 14, 1953 2,645,599 Payne July 14, 1953 

1. A METHOD OF DEWAXING A WAXY OIL WHICH COMPRISES CONTACTING SAID WAY OIL WITH AN INERT ILOTATION GAS AT A FIRST TEMPERATUER (T1), WHEREBY A FIRST WAX-CONTAINING FOAM LAYER AND A FIRST OIL LAYER ARE OBTAINED, SEPARATING SAID FIRST WAX-CONTAINING FOAM LAYER FROM SAID FIRST OIL LAYER, CONTACTING THE WAX AND OIL CONTENT OF SAID FIRST WAXCONTAINING FOAM LAYER WITH AN INERT FLOTATION GAS AT A SECOND TEMPERATURE (T2), WHICH IS HIGHER THAN SAID FIRST TEMPERATURE (T1) BUT AT WHICH A PORTION OF THE WAX IS IN THE SOLID STATE, WHEREBY A SECOND WAX-CONTAINING FOAM LAYER AND A SECOND OIL LAYER ARE OBTAINED, SEPARATING SAID SECOND WAX-CONTAINING FOAM LAYER FROM SAID SECOND OIL LAYER, AND RECYCLING SAID OIL LAYER FOR CONTACT WITH AN INERT FLOTATION GAS AT SAID FIRST TEMPERATURE (T1), THE VISCOSITIES OF THE WAX AND OIL AT THE TEMPERATURES T1 AND T2 BEING MAINTAINED BELOW ABOUT 50 CENTIPOISES. 